The present invention relates to an electroluminescent (hereinafter referred to as "EL") device which emits light by application of a voltage across the electrodes between which a luminescent layer is interposed. More specifically, the invention relates to an EL device in which the terminals of a drive voltage supply are easily connected to the electrodes of the EL device, and which has a low production cost.
In EL devices, when a voltage is applied across the electrodes formed on both surfaces of a luminescent layer, electrons are accelerated by an electric field developing in the luminescent layer, and then collide with luminescent centers existing in the luminescent layer to excite those. The luminescent centers emit light when they return to their ground state. The EL device is constructed by sequentially forming a first electrode, a luminescent layer, an insulation layer and a second electrode on an insulative substrate, and terminals of a voltage supply are connected to the two electrodes to supply a voltage.
The insulation layer between the luminescent layer and the second electrode may be omitted if the luminescent layer is of a dispersion type in which luminescent substances are dispersed in a binder.
Such EL devices are used as a display, an optical printer head, and as a light source of an image reading apparatus. In some cases, the substrate on which the electrodes, luminescent layer, etc. are formed is adhered to the other insulative substrate. An example of this type of EL device is shown in FIGS. 7(a) and 7(b), which is used as a light source of an image reading apparatus.
A transparent electrode 702, luminescent layer 703, insulation layer 704 and non-transparent electrode 705 are formed in sequence on a transparent glass substrate 701 having a thickness of about 50-100 .mu.m.
The transparent glass substrate 701 provided with the EL luminescent layer 703 is adhered to the other insulative substrate 707 provided with light receiving elements 706, by a transparent, insulative adhesive 708 such that the electroluminescent layer 703 and the light receiving elements are opposed to each other. Windows 709 are formed through the luminescent layer 703, insulation layer 704 and non-transparent electrode 705 at their portions opposite to the light receiving elements 706.
In this type of image reading apparatus, while an original document 710 placed on the transparent glass substrate 701 is being scanned, the luminescent layer emits light being driven by a voltage applied across the electrodes 702 and 705, and the emitted light is reflected by the original document surface, passed through the windows 709, and detected by the light receiving elements 706. The light receiving elements 706 convert the detected light to an electrical signal, which serves as image information.
Since the luminescent layer can be located near the original document surface, the above image reading apparatus using the EL device has such advantages that the image reading can be performed satisfactorily even if the luminance of the light source is lower than that of the image reading apparatus using LEDs, etc., and that the apparatus can be made compact.
However, in the conventional EL device, terminals for connecting the voltage supply terminals to the electrodes are formed on the insulative substrate on which the luminescent layer, electrodes, etc. are formed. Therefore, the device is disadvantageous in that it needs much time and labor in fabrication, and that the production cost is high while the manufacturing yield is low.
Particularly in the case of the EL device for use in the image reading apparatus, since transparent glass having a thickness of about 50-100 .mu.m is employed as the insulative substrate on which the luminescent layer and other layers are formed, the insulative layer is so fragile as to cause difficulties in processing it.